CFA is known to contain a variety of metals such as aluminium (Al), titanium (Ti), zinc (Zn), copper (Cu), cobalt (Co), molybdenum (Mo), selenium (Se), boron (B) and many others, usually in the form of insoluble metal-silicates or -oxides (Furuya, K. et al (1987), Environ. Sci. Technol. 21, p.898-903). Many of these metals are toxic to living organisms. Thus, when CFA is disposed of in landfills, in the sea or in other waterways, these metals may leach out of the CFA and enter sources of water for plants and animals including humans. Thus, the various metals contained in CFA represent a potential environmental and health hazard.
Globally, millions of tons of CFA are disposed of annually in industrialised countries, representing a serious potential for environmental pollution and subsequent public health hazard. Power-producing utilities using coal as the energy source are therefore required to safely dispose of the CFA produced as a by-product.
However, the conventional means for detoxifying CFA for the purposes of safely disposing it are both costly and may in themselves also lead to environmental pollution, for example the use of conventional chemical leaching, usually by way of strong acids and at high temperatures (Golden, D. M. (1986) Energy, vol. 11, No. 11/12, p. 1377-1387), requires both costly machinery and chemicals on the one hand, and on the other, chemical by-products, for example strong acids, are produced which must also be disposed of and as such also represent a potential environmental and health hazard.
It has therefore been a long-felt want to establish a process for the detoxification of CFA, by removing therefrom the toxic metals, which is both economically feasible, i.e. allows for the extraction of valuable metals, e.g. aluminium, titanium, cobalt, etc. in commercial quantities, and which does not itself lead to the generation of toxic by-products.
While it has been previously contemplated to use various acid producing bacteria, e.g. Thiobacillus strains in bioleaching methods to extract metals from various metal-bearing sources, none of these methods have been directed specifically to the bioleaching of CFA, nor have any of these methods been successful in generating safely disposable by-products, i.e. they all result in the generation of strong acids which require further expensive and time consuming neutralization treatments.
As noted above, CFA contains a number of toxic metals and thus microorganisms suitable for the bioleaching of CFA must be capable of growing in the presence of these toxic metals.
Furthermore, many coal-fired power stations world-wide are situated at coastal locations with the result that the CFA to be detoxified is often present in sea water, e.g. in consequence of dumping into sea water precipitation pools. Accordingly, microorganisms suitable for bioleaching this CFA must also be capable of growing in a sea water environment, i.e. in the presence of a relatively high salt concentration.
It has heretofore not been disclosed that an acid-producing microorganism suitable for the bioleaching of CFA, e.g. a Thiobacillus strain may be obtained that is capable of growing in a sea water based medium in the presence of CFA.